The House would be in uncharted waters if McCarthy is removed as speaker: A motion to vacate has never been used successfully.

But the chamber wouldn't be as paralyzed and chaotic as it was in January amid McCarthy's five-day, 15-ballot vote to win the gavel.

As part of a rule change after 9/11 to support the continuity of government, the speaker is required to deliver to the House clerk an ordered list of members who can act as speaker pro tempore in the event of a vacancy.

The person at the top of McCarthy's list will serve as interim speaker until a new one is elected.

If the motion to vacate is successful, the chamber could go right to another speaker vote -- and McCarthy's allies could put him forward again to reclaim his post.

But unlike in January, it's possible that the House could take up other business in the meantime: The chamber has a rules package, and the speaker pro tempore would have the authority to act as speaker until a new one is elected.

A roll call vote is underway on the motion to vacate, which will decide whether McCarthy will keep his gavel.

If successful, it will be a historic moment. The motion to vacate has only been used once before -- more than a century ago -- and failed.

It would take as few as five Republican defections to oust McCarthy as speaker, if all Democrats vote against him.

House Majority Leader Steve Scalise also stood up to support McCarthy during the debate on the motion to vacate, saying now isn't the time to stop the progress House Republicans have made.

"When we go back to January, as many people have, we knew that it was going to be a narrow majority," Scalise said. "We also knew it wasn't going to be easy. How many of us came here because we thought this job was going to be easy?"

Scalise continued, "One thing we did know is that if we were going to finally start confronting the problems that had been ignored for years and years and years, we had to change the way this place worked. And one thing Speaker McCarthy embraced from Day 1 is to start making those kind of changes to this institution -- opening up the process, allowing members to be more engaged, having amendments come to the floor, single-subject bills, doing appropriations bills."

"Speaker McCarthy has been leading at the top of the level to make sure we have the tools to do our jobs," he added.

Gaetz said earlier this week he'd support Scalise for speaker and believed other Republicans would, too, telling reporters he thinks "very highly" of the No. 2 House Republican.

During the debate, after initially introducing speeches from a few other Republicans who are backing his motion, including Andy Biggs and Bob Good, Gaetz has since used his time to personally respond to each of the pro-McCarthy speeches being made by other lawmakers.

Those responses have sometimes been as brief as simply disputing the common refrain from McCarthy's backers: that moving to oust him is a short-sighted and punitive act that won't help the conference accomplish its goals.

Not so, Gaetz has continually said as he repeats his argument: McCarthy must go.

-ABC News' Adam Carlson

During a more than two-hour caucus meeting, Democrats were strongly encouraged to vote to not support Speaker McCarthy as he fights for his job, sources tell ABC News.

"It is now the responsibility of the GOP members to end the House Republican Civil War," House Minority Leader Hakeem Jeffries said in a statement. "Given their unwillingness to break from MAGA extremism in an authentic and comprehensive manner, House Democratic leadership will vote yes on the pending Republican Motion to Vacate the Chair."

Several Democrats said they don't plan to bail McCarthy out.

"We're not voting in any way that would help save speaker McCarthy," Rep. Pramila Jayapal, D-Wash., said.

Vice Chair of House Democratic caucus Rep. Ted Lieu, D-Calif., said, "the leadership put out the facts and the caucus heard from a lot of members… we need a functioning government and speaker McCarthy has shown he cannot govern."